Change MMC device name to match kernel device tree.

http://b/63889826

Change-Id: I3490a6bb9e5838a06275e83922e4cad1cf26aaaf
(cherry picked from commit 559679c361fe63b455c2f53bdde5823943e95cfa)
diff --git a/drivers/mmc/bcm2835_sdhci.c b/drivers/mmc/bcm2835_sdhci.c
index 3157354..dad56eb 100644
--- a/drivers/mmc/bcm2835_sdhci.c
+++ b/drivers/mmc/bcm2835_sdhci.c
@@ -228,7 +228,7 @@
 }
 
 static const struct udevice_id bcm2835_sdhci_match[] = {
-	{ .compatible = "brcm,bcm2835-sdhci" },
+	{ .compatible = "brcm,bcm2835-mmc" },
 	{ /* sentinel */ }
 };